This invention relates to a position detecting device such as a needle position detecting device which detects a needle position with the aid of a rotor.
FIGS. 12 through 16 shows a conventional sewing machine needle position detecting device disclosed by Japanese Utility Patent Application (OPI) No. 45081-1986 (the term "OPI" as used herein means an "unexamined published application"). In those figures:
Reference numeral 2 designates a spindle for moving a sewing needle up and down. The spindle 2 is rotatably supported by a bearing 1a which is integral with a sewing frame 1.
Reference numeral 3 designates a pulley driven through an endless belt 12 by an electric motor (not shown). The pulley 3 is fixedly mounted on the spindle 2 so that it is rotated together with the belt 12.
Reference numerals 4 and 5 designates a needle lower position indicating board and a needle upper position indicating board, respectively. The boards 4 and 5 are arranged on the inner end face of the pulley 3, which is on the side of the sewing machine frame 1 in such a manner that they are coaxial with the spindle 2 and the board 4 is located outside the board 5. The needle upper position indicating board 5 is secured to the pulley 3 with fixing screws 10 extended through arcuate elongated through-holes 3a which are formed coaxial with the spindle 2. Owing to the elongated through-holes 3a thus formed, the position of the needle upper position indicating board 5 in the direction of rotation can be adjusted from outside the pulley 3. The needle lower position indicating board 4 is held between the pulley 3 and the outer periphery of the needle upper position indicating board 5.
As seen in FIG. 14, the board 4 has a protrusion 4d. The protrusion 4d is engaged with a recess 3b formed in the pulley 3, so that the board 4 is fixed and may not rotate. The needle lower position indicating board 4 has a needle lower position detecting through-hole 4b in the inner peripheral portion thereof, and rotation speed detecting through-holes 4c in the outer peripheral portion thereof. The surface of the needle lower position indicating board except those through-holes is a mirror-finished reflecting surface 4a. As shown in FIG. 16, grooves 3c are formed in the portions of the pulley 3 which confront with the above-described through-holes 4b and 4c in such a manner that the bottoms of the grooves are inclined to the reflecting surface and painted black. Therefore, light is scarcely reflected at the through-holes 4b and 4c.
The needle upper position indicating board 5 has a needle upper position detecting through-hole 5b in the outer peripheral portion, and the surface of the board 5 except the through-hole 5b is formed into a mirror-finished reflecting surface 5a.
In FIG. 15, reference character 6a designates a needle upper position detector confronting with the needle upper position detecting through-hole 5b; 6b, a needle lower position detector confronting with the needle lower position detecting through-hole 4b; and 6c, a rotation speed detector confronting with the rotation speed detecting through-holes 4c. Each of those detectors has a light emitter and a light receiver. The light receiver detects whether or not the output light of the light emitter is reflected; that is, whether the output light is applied to the reflecting surfaces 4a and 5a or to the non-reflecting through-holes 4b, 4c and 5b, and provides a position detection signal.
The detectors 6a, 6b and 6c are mounted on a printed circuit board 9, and are covered with a detector cover 7 in such a manner that only the light emitting surfaces and the light receiving surfaces are exposed. The detector cover 7 is secured through a cover retainer 8 to the bearing 1a with screws 11.
The conventional needle position detecting device is designed as described above. Therefore, in order to adjust the needle upper position indicating board, it is necessary to loosen the screws 10; that is, the adjustment is rather troublesome. Furthermore, the needle lower position indicating board is fixed to the needle upper position indicating board in such a manner that it is not rotatable. Therefore, it is impossible to adjust the needle lower position indicating board separately from the needle upper position detecting board.
The reflecting surface of the needle upper position indicating board is not flush with that of the needle lower position indicating board, and therefore these two boards are different in the distance from the light emitting point to the light receiving point. Accordingly, it is necessary to adjust the positions of the detectors. In the case where the adjustment is not made, the installation of the pulley 3 on the spindle 2 is severe in dimensional tolerance and requires precise adjustment.
Finally, since the non-reflecting surfaces are the through-holes, it is necessary to form the groove in the part of the pulley which confronts with the through-holes in such a manner that its bottom is inclined with respect to the reflecting surface, and to paint the bottom black. Thus, the conventional needle position detector is large in the number of manufacturing steps, being unavoidably expensive.